As the range of activities accomplished with a computer increases, new and innovative ways to provide an interface with a computer are often developed to complement the changes in computer functionality and packaging. For example, touch sensitive screens can allow a user to provide inputs to a computer without a mouse and/or a keyboard, such that desk area is not needed to operate the computer. Examples of touch sensitive screens include pressure sensitive membranes, beam break techniques with circumferential light sources and sensors, and acoustic ranging techniques. However, these types of computer interfaces can only provide information to the computer regarding the touch event, itself, and thus can be limited in application. In addition, such types of interfaces can be limited in the number of touch events that can be handled over a given amount of time, and can be prone to interpret unintended contacts, such as from a shirt cuff or palm, as touch events. Furthermore, touch sensitive screens can be prohibitively expensive and impractical for very large display sizes, such as those used for presentations.
Some interfaces can include imaging equipment to capture silhouette images that correspond to inputs. Such interfaces may include one or more light sources that provide the light to generate the silhouette images against a background. The source or sources of the light may need to be precisely located, and such interfaces typically require a manual calibration step that can be lengthy and can include additional equipment. As a result, such an interface can be expensive, and a setup time for the interface can be complicated and can require a high degree of precision. Furthermore, any change in the interface system (e.g., unintended bump) requires an additional manual calibration.